1. Field of the Invention
The present invention relates to a technology for preventing a telephone number of a regular subscriber in a so-called mobile communication device such as a portable telephone, automobile telephone, and a personal handy phone (PHS) and thereby avoiding an accounting associated with a communication therefrom.
2. Description of the Related Art
In a mobile communication of a portable telephone and an automobile telephone and the like, in order to manage a location information of a communication device and an accounting of a communication fee, it is necessary to transmit the information of a unique identification information of a communication device (SID) and a unique identification information of a subscriber (PID) and the like to a relay station, and the relay station which as received these information will send out a calling signal composed of these identification information and an identification number of a specified telephone call channel to an exchange station. The exchange station will isolate a home memory station of a subscriber from these identification information, then by accessing the subscriber data, will check to see whether it is a regular subscriber who may be allowed to connect. When it is judged of to be connectable, then that telephone call will be permitted.
According to these conventional methods, there have been existed some dangers of being communicated unlawfully with producing a replica, by receiving a dispatched information for the mobile device, deciphering the identification of the SID and PID and the like, then transporting said information to a completely different portable telephone. The encryptions, which will make the decryptions of these dispatched information difficult, have been studied, but prevention of the information decryptions with encryptions has a limitation.